This is not a standard abbreviation in English. I also checked online, and the one and only instance I could find of 'TSU supplement' in this context was on the website of a hotel in Spain. It seems to be related for the supplement for single occupancy of a double or twin room. As there were other errors in the English used on this site, I can only presume that this is a mistake. If you're planning to stay in this hotel, you could ask them what this means. If you're not, I really wouldn't worry about it. What you should be worrying about, though, is a repeated grammatical error in your writing. I wouldn't normally correct writing unbidden, but I'm making an exception here. As you have assessed your English as native-speaker level, you really ought to know that we don't use interrogative word order in embedded questions. Here's your post with the errors corrected: A hotel sent me an email with all the room types and price list, but I couldn't figure out what TSU supplement MEANS or what TSU STANDS for. I already checked in my dictionary and online, but I couldn't find it. Does anybody know what it MEANS, or is there any website that I can look up abbreviations like this?